Witty, 53, will succeed Larry Renfro, who is set to lead UnitedHealth Group’s enterprise growth efforts and Optum’s next-generation investment initiatives through an expanded Optum Ventures. With the appointment, announced last month, Witty stepped down from the UnitedHealth Group board, where he had served as a director since August.

“As I have now seen up close, Optum’s people, expansive capabilities, client focus and culture make it a unique platform from which to advance health care worldwide, so I am incredibly excited to be part of the team,” Witty said.

Optum’s business segments include OptumHealth, the OptumRx PBM and OptumInsight.

Witty joined GSK in 1985 and spent more than three decades with the U.K.-based company. He was appointed as the company’s CEO in 2008 and served in that capacity until last year, when he was succeeded by Emma Walmsley.

In 2012, Witty was awarded a knighthood for services to the U.K. economy and the U.K. pharmaceutical sector.

“We are deeply fortunate in Andrew Witty to have the right person to extend Optum’s momentum and lead the business in its next phase of growth,” David Wichmann, CEO of UnitedHealth Group, said in a statement. “He brings more than three decades of health care system strategic thinking and knowledge from around the globe; a record of fostering innovation and partnerships; seasoned leadership of complex organizations; and a commitment to improving care delivery that will now benefit Optum.”

Witty is one of three high-profile executives from the pharmaceutical industry hired by health care companies in March. CVS Health named Derica Rice, a former chief financial officer of Eli Lilly Co., to lead its CVS Caremark pharmacy benefits management business. And Walgreens Boots Alliance tapped James Kehoe, formerly CFO at Takeda Pharmaceutical Co., as its finance chief.